Is what im doing plagarism?

So i read an online information for an essay i have to write. I read the sentences and re-wrote it by changing a few words around. Is that plagiarism? I also took a sentence straight out of the online source. I know i have to put it in quotes but what do i write in the parenthesis because it doesn't have an author. So do i put (unknown) or the article name in it? MLA Style btw, thank you for your help!